Which of the following best describes a pollutant?
a. a harmful substance that is released to the environment
b. a natural substance that is used by humans or other organisms
c. a substance that is used faster than it can be replaced
d. a substance that is naturally recycled by nature

I think it's A

Explanation:

I actually don't know but the definition of pollutant states that it's a something that is released that harms the environment. I don't know though :)

A harmful substance that is released to the environment

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."